In this application, we outline a set of experiments focusing on the effects of stress-induced release of endogenous opioids on the behavioral responses to cocaine. The application is based on the hypothesis that kappa opioid receptor activation by repeated stress induces release of endogenous dynorphin peptides that underlie a significant component of the stress-induced potentiation of the rewarding properties of cocaine. Results from our preliminary studies have demonstrated that repeated swim stress potentiates cocaine conditioned place preference (CPP) of wild type male C57BI6 mice. Stress-induced potentiation was blocked by the kappa opioid receptor antagonist nor-binaltorphimine (nor-BNI) and was not evident in prodynorphin knockout mice. Results will be extended by determining whether two other stressors (repeated restraint stress and chronic social stress) also produce similar kappa-mediated potentiation. Second, stress-induced reinstatement of cocaine CPP as a model of relapse will be assessed, and the effects of kappa receptor antagonism on stress-induced reinstatement will be determined. We propose to use a phosphospecific antibody to immunolabel brain sections from stressed and unstressed mice with the objective of developing an anatomical assay for activated kappa opioid receptors. The neural pathways containing activated KORs following swim, restraint and social stresses will be compared to define those common circuits likely to mediate endogenous dynorphin regulation of the cocaine response. Lastly, we propose to study the cellular effects of kappa receptor activation on neuronal excitability in the brain regions identified in the previous aim to be potential sites of endogenous opioid action. Brain slices of the identified regions taken from mice previously subjected to the behavioral paradigms defined will be compared by measuring effects of kappa receptor activation on electrophysiological responses from slices from unstressed, control mice. WCVC recordings from cell types will be made. The results should provide essential insight to the possible cellular and molecular mechanisms underlying the regulation of cocaine addiction by kappa opioid systems.